Synchronous rectification circuit and switching power supply thereof

ABSTRACT

The present disclosure relates to a synchronous rectification circuit. Operation states of four transistor switches in the synchronous rectification circuit are adjusted in accordance with a detected input voltage signal of the synchronous rectification circuit to achieve synchronous rectification. Moreover, the transistor switches in a rectifier bridge and a switching control circuit are all integrated into a single chip to have an increased integration level, a reduced chip size, and high efficiency. The present disclosure also relates to a switching power supply comprising the above synchronous rectification circuit.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. application Ser. No.14/521,825, filed on Oct. 23, 2014, which claims the benefit of ChinesePatent Application No. 201310514284.1, filed on Oct. 25, 2013, thecontents of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present disclosure generally relates to the field of powerelectronics, and more particularly, to a synchronous rectificationcircuit adapted to an electronic transformer and a switching powersupply thereof.

BACKGROUND

In a conventional switching power supply, an AC input voltage istypically rectified by a rectifier bridge, such as a full bridge or ahalf bridge. FIG. 1 illustrates a schematic diagram of a rectifierbridge used in a switching power supply. The rectifier bridge, forexample, a full bridge, includes four diodes D1, D2, D3 and D4 which areconnected with each other as an electrical bridge and packaged as achip. In a rectification cycle, the diodes D1 and D4 conduct during apositive half sine wave, and the diodes D2 and D3 conduct during anegative half sine wave. Due to forward conduction characteristics ofthe diodes, an AC input voltage of the switching power supply isconverted into a pulsed DC output voltage which is supplied to thesubsequent power stage 103.

Although the rectifier bridge has a low cost, it has a large size andcauses a power loss which in turn decreases power efficiency.

SUMMARY

One object of the present disclosure is to provide a synchronousrectifier scheme which is adapted to an electronic transformer and usessynchronous rectification switching transistors instead of rectifierdiodes. A switching control circuit controls operation states of thesynchronous rectification switching transistors in accordance with anoutput voltage signal of the electronic transformer to achieve thesynchronous rectification.

According to one aspect of the present disclosure, there is provided asynchronous rectification circuit, comprising: a rectifier bridge havinga first transistor switch, a second transistor switch, a thirdtransistor switch and a fourth transistor switch; and a switchingcontrol circuit configured to generate a first switching signal, asecond switching signal, a third switching signal and a fourth switchingsignal for the first transistor switch, the second transistor switch,the third transistor switch and the fourth transistor switchrespectively, wherein at least one of the first switching signal and thethird switching signal is generated from the second switching signal andthe fourth switching signal.

Preferably, the rectifier bridge receives an input voltage between afirst input terminal, which is a common node between the thirdtransistor switch and the fourth transistor switch, and a second inputterminal, which is a common node between the first transistor switch andthe second transistor switch, and provides an output voltage between afirst output terminal and a second output terminal.

Preferably, the first transistor switch and the second transistor areconnected in series between the first output terminal and the secondoutput terminal, and the third transistor switch and the fourthtransistor are connected in series between the first output terminal andthe second output terminal.

Preferably, the second switching signal is generated in accordance witha second voltage at the second input terminal, and the fourth switchingsignal is generated in accordance with a first voltage at the firstinput terminal.

Preferably, the switching control circuit comprises a first switchingcontrol circuit, a second switching control circuit, a third switchingcontrol circuit, and a fourth switching control circuit for generatingthe first switching signal, the second switching signal, the thirdswitching signal and the fourth switching signal respectively.

Preferably, the second switching control circuit generates a second onsignal for turning on the second transistor switch and a second offsignal for turning off the second transistor switch, as the secondswitching signal, and the fourth switching control circuit generates afourth on signal for turning on the fourth transistor switch and afourth off signal for turning off the fourth transistor switch, as thefourth switching signal.

Preferably, the second switching control circuit comprises a firstvoltage judgment circuit and a second logic circuit, in which the firstvoltage judgment circuit receives the second voltage, compares thesecond voltage with a first threshold voltage and a second thresholdvoltage respectively, and generates a first comparison signal and asecond comparison signal, the second logic circuit receives the firstcomparison signal, the second comparison signal and a dead time signal,generates the second on signal in a case that the second voltage is lessthan the first threshold voltage and the dead time signal is active, andthe second off signal in a case that the second voltage is larger thanthe second threshold voltage; the fourth switching control circuitcomprises a second voltage judgment circuit and a fourth logic circuit,in which the second voltage judgment circuit receives the first voltage,compares the first voltage with a third threshold voltage and a fourththreshold voltage respectively, and generates a third comparison signaland a fourth comparison signal, and the fourth logic circuit receivesthe third comparison signal, the fourth comparison signal and the deadtime signal, generates the fourth on signal in a case that the firstvoltage is less than the third threshold voltage and the dead timesignal is active, and the fourth off signal in a case that the firstvoltage is larger than the fourth threshold voltage.

Preferably, the first switching control circuit generates a first onsignal for turning on the first transistor switch and a first off signalfor turning off the first transistor switch, as the first switchingsignal, and the third switching control circuit generates a third onsignal for turning on the third transistor switch and a third off signalfor turning off the third transistor switch, as the third switchingsignal.

Preferably, the first switching control circuit comprises a first logiccircuit, the first logic circuit receives the second off signal and thefourth on signal, performs an AND operation, and generates the first onsignal; and the first logic circuit receives the second on signal andthe fourth off signal, performs an OR operation, and generates the firstoff signal; the third switching control circuit comprises a third logiccircuit, the third logic circuit receives the second on signal and thefourth off signal, performs an AND operation, and generates the third onsignal; the third logic circuit receives the second off signal and thefourth on signal, performs an OR operation, and generates the third offsignal.

Preferably, the dead time signal represents a time interval during whichboth the second transistor switch and the fourth transistor switch areinactive.

Preferably, the first to fourth transistor switches and the switchingcontrol circuit are integrated into a single integrated chip.

Preferably, the integrated chip comprises four pins for being coupled toperipheral circuits, including two input pins and two output pins.

According to another aspect of the present disclosure, there is provideda switching power supply, comprising a power stage, a driving controlcircuit, and any of the above synchronous rectification circuits.

In the above synchronous rectification circuit, operation states of thefour transistor switches are adjusted in accordance with an inputvoltage signal of the synchronous rectification circuit to achievesynchronous rectification. At least one of the first transistor switchand the third transistor switch is controlled based on operations statesof the second and fourth transistor switches. Thus, the switchingcontrol circuit can have a simplified structure and reliable synchronousrectification effect.

Moreover, the transistor switches in the rectifier bridge and theswitching control circuit may all be integrated into a single chip tohave an increased integration level, a reduced chip size, and highefficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a basic configuration of arectifier bridge used in a switching power supply according to the priorart;

FIG. 2 is a schematic diagram showing an example synchronousrectification circuit adapted to an electronic transformer according tothe present disclosure;

FIG. 3 is a schematic diagram showing details of the switching controlcircuit in FIG. 2; and

FIG. 4 is a waveform diagram showing example operations of thesynchronous rectification circuit according to the present disclosure.

DESCRIPTION OF EMBODIMENTS

Reference will now be made in detail to particular embodiments of thedisclosure, examples of which are illustrated in the accompanyingdrawings. While the disclosure will be described in conjunction with thepreferred embodiments, it will be understood that they are not intendedto limit the disclosure to these embodiments. On the contrary, thedisclosure is intended to cover alternatives, modifications andequivalents that may be included within the spirit and scope of thedisclosure as defined by the appended claims. Furthermore, in thefollowing detailed description of the present disclosure, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present disclosure. However, it will be readilyapparent to one skilled in the art that the present disclosure may bepracticed without these specific details.

Referring now to FIG. 2, a schematic diagram of an example synchronousrectification circuit adapted to an electronic transformer 102 accordingto the present disclosure is shown. In this embodiment, an external ACpower supply is processed by a thyristor 101 and an electronictransformer 102 and is converted into a voltage signal having a sinewave envelope. The voltage signal is then supplied to a synchronousrectification circuit. The synchronous rectification circuit includes afirst transistor switch Q1 and a second transistor switch Q2 which areconnected in series between a first output terminal and a second outputterminal, and a third transistor switch Q3 and a fourth transistorswitch Q4 which are connected in series between the first outputterminal and the second output terminal. The first transistor switch Q1,the second transistor switch Q2, the third transistor switch Q3 and afourth transistor switch Q4 are configured to be a rectifier bridge. Thefirst transistor switch Q1 and the fourth transistor switch Q4constitute a first half bridge, and the second transistor switch Q2 andthe third transistor switch Q3 constitute a second half bridge. Forexample, all of the four transistor switches are N-type MOS transistors.The synchronous rectification circuit further includes a switchingcontrol circuit 201. An AC input voltage of the switching power supplyis converted into a pulsed DC output voltage by four transistorswitches, and is then supplied to a subsequent power stage 103 fordriving a load 104.

Here, a common node between the third transistor switch Q3 and thefourth transistor switch Q4 is a first input terminal L of thesynchronous rectification circuit, and a common node between the firsttransistor switch Q1 and the second transistor switch Q2 is a secondinput terminal N of the synchronous rectification circuit. The first andsecond input terminals receive the input voltage signal from theelectronic transformer 102. Moreover, a common node between the firsttransistor switch Q1 and the third transistor switch Q3 is a firstoutput terminal Vout of the synchronous rectification circuit, and acommon node between the second transistor switch Q2 and the fourthtransistor switch Q4 is a second output terminal GND of the synchronousrectification circuit.

The switching control circuit 201 controls operation states of the fourtransistor switches in accordance with voltages at the first and secondinput terminals. Specifically, the switching control circuit 201includes a first switching control circuit 201-1, a second switchingcontrol circuit 201-2, a third switching control circuit 201-3 and afourth switching control circuit 201-4, for controlling switchingoperations of the first transistor switch Q1, the second transistorswitch Q2, the third transistor switch Q3 and the fourth transistorswitch Q4 respectively.

FIG. 3 is a schematic diagram showing details of the switching controlcircuit 201. The switching control circuit 201 comprises a firstswitching control circuit 201-1, a second switching control circuit201-2, a third switching control circuit 201-3, and a fourth switchingcontrol circuit 201-4 for generating a first switching signal, a secondswitching signal, a third switching signal and a fourth switching signalrespectively, for controlling on and off states of the first transistorswitch Q1, the second transistor switch Q2, the third transistor switchQ3 and a fourth transistor switch Q4 respectively.

The second switching control circuit 201-2 includes a first voltagejudgment circuit and a second logic circuit. The first voltage judgmentcircuit receives a voltage V_(N) at the second input terminal, comparesthe voltage V_(N) with a first threshold voltage V_(th1) and a secondthreshold voltage V_(th2) respectively, and generates a first comparisonsignal and a second comparison signal. Here, the first threshold voltageV_(th1) is less than zero. Preferably, the first threshold voltageV_(th1) in this embodiment is −30 mV. The second threshold voltageV_(th2) is larger than zero. Preferably, the second threshold voltageV_(th2) in this embodiment is 10 mV.

The second logic circuit receives the first comparison signal, thesecond comparison signal and a dead time signal V_(dead time), generatesa second on signal S_(Q2-on) for turning on the second transistor switchin a case that the voltage at the second input terminal is less than thefirst threshold voltage and the dead time signal V_(dead time) isactive, and a second off signal S_(Q2-off) for turning off the secondtransistor switch in a case that the voltage at the second inputterminal is larger than the second threshold voltage. The dead timesignal V_(dead time) represents a time interval during which both thesecond transistor switch and the fourth transistor switch are inactive.

Specifically, the first voltage judgment circuit in this embodimentincludes a first sampling circuit 202, a first comparator and a secondcomparator, and the second logic circuit includes a first AND circuitand a second flip-flop. The second switching control circuit may beother circuits having the same function.

The fourth switching control circuit 201-4 includes a second voltagejudgment circuit and a fourth logic circuit. The second voltage judgmentcircuit receives a voltage V_(L) at the first input terminal, comparesthe voltage V_(L) with a third threshold voltage V_(th3) and a fourththreshold voltage V_(th4) respectively, and generates a third comparisonsignal and a fourth comparison signal. The fourth logic circuit receivesthe third comparison signal, the fourth comparison signal and a deadtime signal V_(dead time), generates a fourth on signal S_(Q4-on) forturning on the fourth transistor switch in a case that the voltage atthe first input terminal is less than the third threshold voltage andthe dead time signal V_(dead time) is active, and a fourth off signalS_(Q4-off) for turning off the fourth transistor switch in a case thatthe voltage at the first input terminal is larger than the fourththreshold voltage. Similarly, the third threshold voltage V_(th3) isless than zero. Preferably, the third threshold voltage V_(th3) in thisembodiment is −30 mV. The fourth threshold voltage V_(th4) is largerthan zero. Preferably, the fourth threshold voltage V_(th4) in thisembodiment is 10 mV.

Specifically, the second voltage judgment circuit in this embodimentincludes a second sampling circuit 204, a third comparator and a fourthcomparator, and the fourth logic circuit includes a second AND circuitand a fourth flip-flop. The fourth switching control circuit may beother circuits having the same function.

The first switching control circuit 201-1 includes a first logiccircuit. The first logic circuit receives the second off signalS_(Q2-off) and the fourth on signal S_(Q4-on), performs an ANDoperation, and generates a first on signal S_(Q1-on) for turning on thefirst transistor switch. The first logic circuit receives the second onsignal S_(Q2-on) and the fourth off signal S_(Q4-off), performs an ORoperation, and generates a first off signal S_(Q1-off) for turning offthe first transistor switch.

Specifically, the first logical circuit includes a third AND gate, afirst OR gate and a first flip-flop. The first switching control circuitmay be other circuits having the same function.

The third switching control circuit 201-3 includes a third logiccircuit. The third logic circuit receives the second on signal S_(Q2-on)and the fourth off signal S_(Q4-off), performs an AND operation, andgenerates a third on signal S_(Q3-on) for turning on the thirdtransistor switch. The third logic circuit receives the second offsignal S_(Q2-off) and the fourth on signal S_(Q4-on), performs an ORoperation, and generates a third off signal S_(Q3-off) for turning offthe third transistor switch.

Specifically, the third logical circuit includes a fourth AND gate, asecond OR gate and a third flip-flop. The third switching controlcircuit may be other circuits having the same function.

Operations of the synchronous rectification circuit in this embodimentwill be described below, in combination with a waveform diagram in FIG.4, showing example operations of the synchronous rectification circuitaccording to the present disclosure, and the above schematic diagramshowing details of the synchronous rectification circuit.

In FIG. 4, the waveform V_(L) is a voltage waveform at the first inputterminal, and the waveform V_(N) is a voltage waveform at the secondinput terminal. At time t1, the voltage V_(L) at the input terminal Lincreases. Body diodes of the second and third transistor switchesconduct when a voltage drop between the voltage V_(L) and the voltageV_(N) is larger than a sum of conduction voltage drops of the bodydiodes of the second and third transistor switches. Meanwhile, thesecond transistor switch Q2 has a negative drain to source voltage. Itshould be noted that the voltage V_(N) is the drain to source voltage ofthe second transistor switch Q2. When the first voltage judgment circuitdetects that the voltage V_(N) is less than the first threshold voltageV_(th1), the first comparison signal is inverted to a high level. Thesecond switching control circuit 201-2 turns on the second transistorswitch Q2 until time t2, during which the dead time signal V_(dead time)is active. Meanwhile, the fourth transistor switch Q4 is in an offstate, and the third switching control circuit 201-3 turns on the thirdtransistor switch Q3. At time t3, when the first voltage judgmentcircuit detects that the voltage V_(N) is larger than the secondthreshold voltage V_(th2), the second comparison signal is inverted to ahigh level. The second switching control circuit 201-2 turns off thesecond transistor switch Q2. Meanwhile, the third switching controlcircuit 201-3 turns off the third transistor switch Q3. Consequently, afirst half sine wave is outputted at the output terminal of thesynchronous rectification circuit.

At time t3, the voltage V_(N) at the input terminal N then increases.Body diodes of the fourth and first transistor switches is turned onwhen a voltage drop between the voltage V_(N) and the voltage V_(L) islarger than a sum of conduction voltage drops of the body diodes of thefourth and first transistor switches. Meanwhile, the fourth transistorswitch Q4 has a negative drain to source voltage. It should be notedthat the voltage V_(L) is the drain to source voltage of the fourthtransistor switch. When the second voltage judgment circuit detects thatthe voltage V_(L) is less than the third threshold voltage V_(th3), thethird comparison signal is inverted to a high level. The fourthswitching control circuit 201-4 turns on the fourth transistor switch Q4until time t4, during which the dead time signal V_(dead time) isactive. Meanwhile, the second transistor switch Q2 is in an off state,and the first switching control circuit 201-1 turns on the firsttransistor switch Q1. At time t5, when the second voltage judgmentcircuit detects that the voltage V_(L) is larger than the secondthreshold voltage V_(th2), the fourth comparison signal is inverted to ahigh level. The fourth switching control circuit 201-4 turns off thefourth transistor switch Q4. Meanwhile, the first switching controlcircuit 201-1 turns off the first transistor switch Q1. Consequently, asecond half sine wave is outputted at the output terminal of thesynchronous rectification circuit.

The AC output voltage from the electronic transformer 102 is rectifiedby the above synchronous rectification circuit to obtain a pulsed DCoutput voltage. Here, the first to fourth transistor switches Q1-04 andthe switching control circuit 201 may be integrated into a singleintegrated chip. It should be noted that a bootstrap capacitor may bearranged outside the chip for each of the first transistor switch Q1 andthe third transistor switch Q3 so that a voltage drop is applied asrequired between a gate and a source of the respective transistorswitch. In an actual circuit operation, a gate driver may be arrangedfor each of the first transistor switch Q1 and the third transistorswitch Q3 so that a gate to source voltage of the respective transistorswitch can reach a conduction threshold voltage.

As discussed above, the synchronous rectification circuit according tothe present disclosure converts an AC input voltage to a DC outputvoltage by four transistor switches. The control circuit is simple andhas high efficiency. The chip size is also reduced by integrating moreelectronic devices in a single integrated chip. In the embodiments ofthe present disclosure, various electronic devices of the synchronousrectification circuit are encapsulated in a single semiconductor chip.The integrated chip has four pins for being coupled to peripheralcircuits, including two input pins and two output pins. The two inputpins correspond to the first and second input terminals of thesynchronous rectification circuit, and two output pins correspond to thefirst and second output terminals of the synchronous rectificationcircuit. Compared with the conventional rectifier bridge using fourdiodes, the synchronous rectification circuit decreases the size of therectification bridge and the number of the pins. The synchronousrectification circuit according to the present disclosure is used forrectifying a voltage signal having a sine wave envelope from anelectronic transformer 102, but not limited to this.

According to another aspect of the present disclosure, there is provideda switching power supply, comprising a power stage, a driving controlcircuit, and the above synchronous rectification circuits. Similarly,the switching power supply advantageously has high efficiency and areduced size.

The synchronous rectification circuit adapted to the electronictransformer according to the present disclosure has been described indetail for the preferable embodiments. It is apparent for one skilledperson that other technique or configuration or circuits or electronicdevices, if being equivalents, can also be used in these embodiments.

Although various embodiments of the present disclosure are describedabove, these embodiments neither present all details, nor imply that thepresent disclosure is limited to these embodiments. Obviously, manymodifications and changes may be made in light of the teaching of theabove embodiments. These embodiments are presented and some details aredescribed herein only for explaining the principle of the disclosure andits actual use, so that one skilled person can practice the presentdisclosure and introduce some modifications in light of the disclosure.The disclosure is intended to cover alternatives, modifications andequivalents that may be included within the spirit and scope of thedisclosure as defined by the appended claims.

What is claimed is:
 1. A synchronous rectification circuit, comprising:a rectifier bridge having a first transistor switch, a second transistorswitch, a third transistor switch and a fourth transistor switch; and aswitching control circuit configured to generate a first switchingsignal, a second switching signal, a third switching signal and a fourthswitching signal for said first transistor switch, said secondtransistor switch, said third transistor switch and said fourthtransistor switch respectively, wherein said first switching signal andsaid third switching signal are different signals, and at least one ofsaid first switching signal and said third switching signal is generatedfrom both of said second switching signal and said fourth switchingsignal, wherein said rectifier bridge receives an input voltage betweena first input terminal, which is a common node between said thirdtransistor switch and said fourth transistor switch, and a second inputterminal, which is a common node between said first transistor switchand said second transistor switch, and provides an output voltagebetween a first output terminal and a second output terminal, whereinsaid switching control circuit comprises a first switching controlcircuit, a second switching control circuit, a third switching controlcircuit, and a fourth switching control circuit for generating saidfirst switching signal, said second switching signal, said thirdswitching signal and said fourth switching signal respectively, whereinsaid second switching control circuit generates a second on signal forturning on said second transistor switch and a second off signal forturning off said second transistor switch, as said second switchingsignal, and said fourth switching control circuit generates a fourth onsignal for turning on said fourth transistor switch and a fourth offsignal for turning off said fourth transistor switch, as said fourthswitching signal, said first switching control circuit generates a firston signal for turning on said first transistor switch and a first offsignal for turning off said first transistor switch, as said firstswitching signal, and said third switching control circuit generates athird on signal for turning on said third transistor switch and a thirdoff signal for turning off said third transistor switch, as said thirdswitching signal, wherein said first switching control circuit comprisesa first logic circuit, said first logic circuit receives said second offsignal and said fourth on signal, performs an AND operation, andgenerates said first on signal; and said first logic circuit receivessaid second on signal and said fourth off signal, performs an ORoperation, and generates said first off signal; said third switchingcontrol circuit comprises a third logic circuit, said third logiccircuit receives said second on signal and said fourth off signal,performs an AND operation, and generates said third on signal; saidthird logic circuit receives said second off signal and said fourth onsignal, performs an OR operation, and generates said third off signal.2. The synchronous rectification circuit according to claim 1, whereinsaid first transistor switch and said second transistor switch areconnected in series between said first output terminal and said secondoutput terminal, and said third transistor switch and said fourthtransistor switch are connected in series between said first outputterminal and said second output terminal.
 3. The synchronousrectification circuit according to claim 1, wherein said secondswitching signal is generated in accordance with a second voltage atsaid second input terminal, and said fourth switching signal isgenerated in accordance with a first voltage at said first inputterminal.
 4. The synchronous rectification circuit according to claim 3,wherein said second switching control circuit comprises a first voltagejudgment circuit and a second logic circuit, in which said first voltagejudgment circuit receives said second voltage, compares said secondvoltage with a first threshold voltage and a second threshold voltagerespectively, and generates a first comparison signal and a secondcomparison signal, said second logic circuit receives said firstcomparison signal, said second comparison signal and a dead time signal,generates said second on signal in a case that said second voltage isless than said first threshold voltage and said dead time signal isactive, and said second off signal in a case that said second voltage islarger than said second threshold voltage; said fourth switching controlcircuit comprises a second voltage judgment circuit and a fourth logiccircuit, in which said second voltage judgment circuit receives saidfirst voltage, compares said first voltage with a third thresholdvoltage and a fourth threshold voltage respectively, and generates athird comparison signal and a fourth comparison signal, and said fourthlogic circuit receives said third comparison signal, said fourthcomparison signal and said dead time signal, generates said fourth onsignal in a case that said first voltage is less than said thirdthreshold voltage and said dead time signal is active, and said fourthoff signal in a case that said first voltage is larger than said fourththreshold voltage.
 5. The synchronous rectification circuit according toclaim 4, wherein said dead time signal represents a time interval duringwhich both said second transistor switch and said fourth transistorswitch are inactive.
 6. The synchronous rectification circuit accordingto claim 1, wherein said first to fourth transistor switches and saidswitching control circuit are integrated into a single integrated chip.7. The synchronous rectification circuit according to claim 6, whereinsaid integrated chip comprises four pins for being coupled to peripheralcircuits, including two input pins and two output pins.
 8. A switchingpower supply, comprising a power stage and said synchronousrectification circuit according to claim
 1. 9. The synchronousrectification circuit according to claim 1, wherein said rectifierbridge converts an AC input voltage between a first input terminal and asecond input terminal into a pulsed DC output voltage between a firstoutput terminal and a second output terminal.